Solid dispersions are of use for an enhanced solubility of drugs or for controlling the rate of release of a drug from a dosage form or improving the bioavailability of drugs, thus being of significant commercial value.
The conventional technology for the production of a solid dispersion includes a fusion process which is characterized by melting a drug and a polymer together at elevated temperature and, then, cooling the melt to solidify, a solvent process which is characterized by dissolving a drug and a polymer in an appropriate solvent and, then, removing the solvent, and a fusion-solvent process which has the characteristics of said processes.
However, the fusion process has the disadvantage that it cannot be applied to a drug or polymer which is, or is likely to be, thermally degraded.
The solvent process is free from the above-mentioned disadvantage of the fusion process but because it employs an organic solvent such as an alcohol or a chlorine-containing solvent, this process has the following disadvantages.
(1) When an alcohol is used as the solvent, strict measures must be provided for the prevention of an explosion hazard during production.
(2) Since organic solvents have fairly high affinities for the polymer, they cannot be easily removed from the product solid dispersions.
(3) Removal of the solvent necessarily results in its diffusion into the atmosphere to cause an atmospheric pollution.
(4) After removal of the solvent, the solid dispersion adhering intimately to the vessel wall cannot be easily withdrawn from the vessel.